The present invention relates to a surface mounted (SMD) electronic parts capable of being surface-mounted on a circuit board for an electronic device and a method for manufacture therefore. More particularly, relates to the terminal structure of the small-sized surface mounted electronic parts in which a through hole or a blind hole having an electrode film on an inner surface thereof is cut by the dicing processing to form an external connection terminal of substantially semicircular concave arc shape.
There is a known technique that many same electronic parts functions are formed on a substrate made from resin or the like, through hole electrodes or blind hole electrodes are formed at the boundary portions of the electronic parts functions, and the many same electronic parts functions are divided with reference to the center lines of the through holes or blind holes to form respective electronic parts. However, the miniaturization of the electronic parts has been demanded in the market and further due to the following reasons, there are many cases that the dividing processing must be performed by means of dicing cutting processing using a blade rotating at a high speed.
That is, there has arisen needs for reducing the diameter of a through hole (or blind hole); and since the external connection terminal formed by dividing the through hole (or blind hole) having an electrode film formed on an inner wall thereof through plating processing is required to have stable connection quality even with a small connection (formed through soldering in general) area, the terminal is required to have high shape accuracy and-high surface accuracy.
As other dividing processings, there are the bending processing (chocolate breaking processing), end milling processing (router processing), press cutting processing, or the like. However, in many cases, such other dividing processings are not suitable in view points of quality and economy as the dividing processing for dividing a small and precise electronic parts chip.
Conventionally, at the time of cutting and dividing a substrate on which many same electronic parts functions are formed, there has been employed a method and structure that the through hole (or blind hole) is cut into two parts each forming a just semicircular shape or that the through hole (or blind hole) is cut by making the center position of the through hole (or blind hole) coincide with the center position of the blade thickness of the cutting blade thereby to use the both of the divided electrode films of the through hole (or blind hole) as the electrode of the products (electronic parts).
However, according to such a method or structure that the through hole (or blind hole) is cut into two parts each forming a just semicircular shape or a method or structure that the through hole (or blind hole) is cut by making the center position of the through hole (or blind hole) coincide with the center position of the blade thickness of the cutting blade, burr is likely generated at the cross section of the electrode film, that is, the metal film formed through plating processing on the inner-surface of the through hole and so it is difficult to obtain precise and uniform cross section. The quality of the connection portion at the time of connecting the electronic parts (through the soldering process or the like) to the external circuit is degraded due to the burr generated at the cross section, that is, the surface of the external connection terminal. Further, since the burrs are mechanically unstable, some of burrs may be come off by applying slight force thereto despite that some of burrs are tightly adhered to the terminal surface. The burr thus come off may cause such a problem that the burr short-circuits the patterns of the circuit board of the various types of devices on which electronic parts are mounted thereby to degrade the entire reliability of the device.
The known document Japanese Patent Publication 2-213196 proposes a manufacturing method of a substrate having through holes at the end surfaces thereof, in that a through hole and a substrate are divided without causing the chip off or cracking of the plated layer formed on the inner surface of the through hole. However, such a method requires, in a process preceding to the dividing process of the substrate by using a die, a process of removing the plated layer formed on the inner wall of a through hole at the non-product side by means of the boring process, and so the manufacturing process is complicated.